Some modern processes for recovering lead from sulphide ores and concentrates include the Kivcet process, the QSL process, the SKS process and the ISASMELT™ process. Part of the world's primary lead production is made using these processes, and part is made from the conventional flowsheet of a sinter plant and blast furnace.
The ISASMELT™ process utilises gas injection into melts via a top entry submerged lance. Injection of gases via the top entry submerged lance produces a very turbulent bath in which high intensity smelting or reduction reactions take place. In the ISASMELT™ process, a two stage process may be utilised. In the two stage process, lead concentrate is added directly to a molten slag bath in a smelting furnace. This produces a lead containing slag, which is transferred to a second furnace in which that lead containing slag is reduced to form lead bullion. Both furnaces use top entry submerged lances for injection of gases.
The ISASMELT™ process can also be used to directly reduce some of the concentrate added to the smelting furnace to lead bullion. Typically, concentrates containing high levels of lead, such as between 55% to 80%, but more preferably between 60% to 75% have been processed in this manner, although concentrates having lead concentrations outside this range may also be processed using direct smelling.
In the production of zinc, zinc containing ores and concentrates can be subjected to a leaching process in order to solubilise zinc values. The dissolved zinc is separated from the leach residue and the pregnant leach liquor containing dissolved zinc is treated to recover zinc.
The Albion Process™ is an oxidative leaching process that can be used to treat zinc sulphide ores and concentrates. Zinc sulphide ores and concentrates normally also contain lead. Following the leaching step in the Albion Process™, a solid residue is recovered which contains lead (typically in the form of lead compounds, especially lead sulphide and lead sulphate) and high amounts of elemental sulphur. For example, the leach residue may contain from 15 to 25% lead and at least 30% elemental sulphur, for example, from 40 to 60% elemental sulphur. Other leaching processes may also result in the formation of leach residues containing lead and high levels of elemental sulphur. Some silver may also be present in the leach residue.
Solid residues containing such high levels of elemental sulphur have proven to be difficult to process. These residues have a very different chemical composition to the lead sulphide concentrates that are normally processed to produce lead. Due to the difficulties in processing solid residues containing such high levels of elemental sulphur, the solid residues have, up to now, lacked an effective treatment route, and have been stored in tailings dams or tailings piles.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.
Throughout this specification, the word “comprising” and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicate otherwise